Modification of spastic stretch reflexes at the elbow by flexion synergy expression in individuals with chronic hemiparetic stroke

Publication date: Available online 24 July 2017
Source:Archives of Physical Medicine and Rehabilitation
Author(s): Jacob G. McPherson, Arno H.A. Stienen, Justin M. Drogos, Julius P.A. Dewald
ObjectiveTo systematically characterize the impact of flexion synergy expression on the manifestation of elbow flexor stretch reflexes post-stroke, and to relate these findings to elbow flexor stretch reflexes in individuals without neurological injury.DesignControlled cohort study.SettingAcademic medical center.ParticipantsTen individuals with chronic hemiparetic stroke and a convenience sample of 10 individuals without neurological or musculoskeletal injury.InterventionsParticipants with stroke were interfaced with a robotic device that precisely manipulated flexion synergy expression (by regulating shoulder abduction loading) while it delivered controlled elbow extension perturbations over a wide range of velocities. This device was also used to elicit elbow flexor stretch reflexes during volitional elbow flexor activation, both in the cohort of individuals with stroke and in a control cohort. In both cases, the amplitude of volitional elbow flexor pre-activation was matched to that generated involuntarily during flexion synergy expression.Outcome measuresThe amplitude of short and long latency stretch reflexes in the biceps brachii, assessed by electromyography, and expressed as a function of background muscle activation and stretch velocity.ResultsIncreased shoulder abduction loading potentiated elbow flexor stretch reflexes via flexion synergy expression in the paretic arm. Compared to stretch reflexes in individuals without neurological injury, paretic reflexes were larger at rest but were approximately equal to control muscles at matched levels of pre-activation.ConclusionsBecause flexion synergy expression modifies stretch reflexes in involved muscles, interventions that reduce flexion synergy expression may confer the added benefit of reducing spasticity during functional use of the arm.



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